SUBSEA PRODUCTION MANIFOLD

Abstract: There is disclosed a production manifold for use in the oil/gas industry, particularly for subsea use. Known manifolds suffer from a number of problems such as high capital cost, operating expenditure and the requirement of a dedicated test header. The present invention therefore provides an oil/gas production manifold (100) comprising first and second headers (145, 150) each of which is controllably communicable with at least one production well via control means (155, 160, 165), an outlet end of each header being connectable to a respective pipeline (280, 315), wherein the headers are connected to and communicable with one another by a pigging line (285).

Description: Subsea production manifold. This invention relates to a production manifold for use in the oil/gas industry, and in particular to a subsea production manifold. Subsea production manifolds are known. Their function is to collect and commingle production of oil/gas from a number of satellite wells via a header system to export such therefrom to platform facilities, or the like, where the produce may be subjected to various stages of treatment and conditioning. During the life of an oil/gas field the condition of satellite wells requires to be monitored by performing well tests. Such tests may be made by isolating production of the well under test from the remaining wells and measuring the pressure drop over a period of time. By measuring the pressure drop, along with analysis of components of flow (gas/oil/water) , production of a well can be analysed and remedial action taken to seek to optimise production, if required. The above dictates that pipelines to and from the manifold facilitate pig operations for cleaning pipelines prior to test so as to ensure that the line is free from wax, sand or other contaminants which would affect the test results. A known subsea production manifold is illustrated in Fig 1. Therein, the manifold 5 routes production from any of, for example, ten wells (not shown) via inlet ports 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 through one of two production headers 65,70. A test header 75 is provided for testing the production of any of the wells 15-60. Pigging operations may be performed through a 'Y' (WYE) junction 80. An alternative to the WYE 75 is the introduction of a subsea pig launcher into the system. This is placed at the start of the test header and pigs launched from it to the platform. However, this not only attracts a capital cost during fabrication but a considerable OPEX (operating expenditure) cost during field life. OPEX - a recognised term in the oil/gas industry - are the costs associated with the running of a development. In this case it would include the DSV (Diving Support Vessel) and offshore time involved. A further disadvantage to the prior art is the requirement for the provision of a dedicated test header, and associated pipeline linking the manifold to a platform, which is used only during testing operations. It is an object of the present invention to obviate or mitigate the aforementioned disadvantages in the prior art. It is a further object of the present invention to provide a manifold of a simpler construction and having a reduced number of valves on the test line than previously known manifolds. According to a first aspect of the present invention there is provided an oil/gas production manifold comprising first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line. This manifold is particularly advantageous over the prior art since it obviates the need for a separate test header. Preferably the first and second ends of the pigging line are connected to the outlet ends of the first and second headers respectively. A preferred embodiment of the invention is suitably adapted for subsea use. Each header may be connectable to a respective pipeline and connected to the pigging line by means of a three-way joint. Preferably the pigging line is provided with a valve, which may be a hydraulically actuated valve with ROV (Remote Operated Vehicle) override. The headers may further be connected to and communicable with one another by a further line having a further valve provided therein. The further line may be provided at or near ends of the headers remote from the outlet ends. In a preferred embodiment of the invention the manifold comprises first and second headers each of which is controllably communicable with ten production wells. According to a second aspect of the present invention, there is provided a method of collecting oil/gas produced from at least one production well into a manifold, wherein the manifold comprises first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line. According to a third aspect of the present invention there is provided a method of testing production from an oil/gas well fed via a production manifold comprising first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line, the pigging line having a valve therein, the method comprising closing the valve, controllably communicating the well with the first/second header and controllably communicating any/all other wells with the second/first header. In this way production from any well can be isolated and tested as required. According to a fourth aspect of the present invention there is provided a method of pigging first and second oil/gas production pipelines, each pipeline being connected to an outlet end of a respective first/second header of a production manifold, the manifold comprising, first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line, the pigging line having a valve therein and the outlets having respective valves provided at or near thereto, the method comprising closing the respective valves, opening the valve in the pigging line and launching a pig down the first/second pipeline through the pigging line and up the second/first pipeline. An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, which are: Fig 1 a schematic plan view of a known subsea production manifold; Fig 2 a schematic plan view of an embodiment of a subsea production manifold according to the present invention; and Fig 3 a simplified schematic perspective view of the manifold of Fig 2. Referring to Figs 2 and 3 there is illustrated an embodiment of a subsea oil/gas production manifold, generally designated 100, for collecting production from ten wells (not shown) connected to the manifold 100 by respective inlet ports 105, 110, 115, 120, 125, 130, 135, 140, 141, 142. The manifold 100 comprises first and second header pipes (headers) 145, 150 each of which is controllably communicable with each well via control means in the form of an inlet arm 155 and first and second outlet arms 160, 165. The inlets 105 - 140 are the inlets to the inlet arms 155, while outlets from the first and second outlet arms 160, 165 are connected to the first and second headers 145, 150 respectively via flange joints 151, 152. The inlet arm 155 comprises a flexible pipe 170 an outermost end of which is connectable to the respective well, and a second end of which is connected to a first length of rigid pipework 180 via a flange connection 185. Provided along the pipework 180 is a pressure sensor 186 connected to the pipework 180 by a flange joint 190. A reducer 195 is provided for connecting the pipework 180 to one end of a first hydraulically actuated choke valve 200 having ROV (Remote Operated Vessel) override. Another end of the valve 200 is connected via a further reducer 201 to one end of a second length of rigid pipework 205 having a temperature sensor 210 connected thereto by a flange joint 215. The other end of the pipework 205 is connected to one end of a one-way check valve 220. The other end of the check valve 220 is connected to the two outlet arms 160, 165. The first outlet arm 160 comprises pipework 225 having a second hydraulically actuated valve 230 with ROV override, a first manual/ROV operated valve 235 and between the valves 230, 235 a block and bleed valve 240. Similarly, the second outlet arm 165 comprises pipework 250 having a further second hydraulically actuated valve 255 with ROV override, a further first manual/ROV operated valve 260 and between the valves 255, 260 a block and bleed valve 265. Each outlet arm 160, 165 may be provided with a sand probe 275 which is a known device for detecting excessive levels of sand or the like. The purpose of the various valves of the control means is as follows: the hydraulically actuated choke valve 200 controls the back pressure from the well into the manifold 100; the one-way check valve ensures one way flow through the control means; the hydraulically actuated valves 230, 255 control production flow from the well to the respective headers 145, 150 and thence to the platform; the manual/ROV operated valves 235, 260 in conjunction with the hydraulically actuated valves 230, 255 can be used to isolate pipework between the valves 230, 235 and 255, 260 so as to allow the bleed valves 240, 265 to be operated for maintenance purposes. A first/output end of the first header 145 is connectable to a first pipeline 280 and connected to a pigging line 285 via a pigging tee joint 290. Provided at or near the first end of the first header is a header hydraulically actuated valve 300 with ROV override. Provided along the first header 145 and connected thereto via flange joints 305 is a pressure sensor 310 and scale/corrosion inhibitor injection assemblies 315. Similarly, a first output end of the second header 150 is connectable to a second pipeline 315 and connected to the pigging line 285 via a pigging tee joint 320. Provided at or near the first end of the second header 150 is a header hydraulically actuated valve 325 with ROV override. Provided along the second header 150 and connected thereto via flange joints 330 is a pressure sensor 335 and scale/corrosion inhibitor injection assemblies 340. Provided in the pigging line 285 is a pigging hydraulically actuated valve 345 with ROV override. The purpose of the header hydraulically actuated valves 300, 325 is to isolate the respective header 145, 150 from the respective pipeline 280, 315. The purpose of the pigging valve 345 is to controllably provide a pigging loop from one pipeline 280, 315 to the other pipeline 315, 280 via the pigging line 285. Provided at a second end of the first header 145 is a flange joint 350. Similarly, provided at a second end of the second header 150 is a flange joint 355. The flange joints 350, 355 allow the headers 145, 150 of the manifold 100 to be connected to further pipework or the like, such as a further production manifold. Provided between and connected to the headers 145, 150 at or near their second ends is an isolation/balance line 360 having an isolation/balance hydraulically actuated valve 365 with ROV override suitably connected in the line 360 by reducers 370, 375. The purpose of the isolation/balance valve 365 is when closed to isolate the headers 145, 150 from one another, and when open to balance flow from and between the headers 145, 150. The hydraulically operated valves 200, 230, 255, 300, 325, 345, 365 may be controlled remotely from a platform or the like. The pipework of the control means may be 6" in nominal diameter, while the headers 145, 150 may be 12" in nominal diameter, the pigging line 285 may be 12" in nominal diameter and the pipelines 280, 315 may be 12" in nominal diameter. In normal production use, the hydraulically actuated choke valve 200 will be open as will the manual/ROV operated valves 235, 260 in both arms 160, 165. Production flow through one outlet arm 160/165 to one header 145/150 will be allowed by opening of the hydraulically actuated valve 230/255 in that arm 160/165, while flow through the other arm 160/165 to the other header 150/145 will be prevented by closure of the hydraulically actuated valve 255/230 in that arm 165/160. The header hydraulically actuated valve 300/325 of the one header 145/150 will be opened, while the pigging valve 345 will be closed. The isolation/balance valve 365 may or may not be opened. In this way flow from any given well may selectively and controllably pass to one of the pipelines 280/315 via the respective header 145/150 of the manifold 100. In order to test production from one of the wells production from that well is controllably passed to one of the headers 145/150 which acts as a test header while production from the other wells is isolated from that header 145, 150, and may be passed to the other header 150, 145. In this mode of operation the header valve 300, 325 of the header 145, 150 acting as the test header is open to allow production flow up the respective pipeline which then acts as the test pipeline. Also in this mode, the pigging valve 345 is closed, as is the isolation/balance valve 365. In pigging mode the header hydraulically actuated valves 300, 325 are closed and the pigging valve 345 opened. A pigging loop from pipeline to pipeline via the pigging line 285 is thereby provided. In summary, production from all wells may be routed through control means (well bay piping) into the two headers. The headers have a dual function acting as production headers during normal operation and production/test headers as and when required. In the event of a well test one of the manifold headers, and the pipeline connected to it, is designated for test. All connections to that header from the wells apart from the one under test, are closed and total manifold production routed through the other header for the duration of the test. The requirement for on-line inspection and round trip pigging is accommodated with provision of a pigging loop in the pipe system. This is sized, as is the header, to accommodate the production from the remaining wells. During well testing the isolation valve in this pigging loop is closed separating the test and production flow streams to the platform. Provision for test flow offtake to a test separator will be required in the topsides piping arrangement. It should be understood that the embodiment of the present invention hereinbefore described is given by way of example only, and is not meant to limit the scope of the invention in any way. Particularly it should be understood that advantages of the invention include: elimination of a dedicated test header and pipeline system linking manifold at the development to the platform facilities; reduced OPEX when required to pig the test line obviating the need to mobilise a DSV to install a subsea pig launcher; and simiplified piping configuration and reduction in the number of valves required on the test line.

Claims: Claims 1. An oil/gas production manifold comprising first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line. 2. An oil/gas production manifold as claimed in claim 1, wherein the first and second ends of the pigging line are connected to the outlet ends of the first and second headers respectively. 3. An oil/gas production manifold as claimed in any preceding claim, wherein the manifold is suitably adapted for subsea use. 4. An oil/gas production manifold as claimed in any preceding claim, wherein each header is connectable to a respective pipeline and connected to the pigging line by means of a three-way joint. 5. An oil/gas production manifold as claimed in any preceding claim, wherein the pigging line is provided with a valve which may be a hydraulically actuated valve with ROV (Remote Operated Vehicle) override. 6. An oil/gas production manifold as claimed in any preceding claim, wherein the headers are further connected to and communicable with one another by a further line having a further valve provided therein. 7. An oil/gas production manifold as claimed in claim 6, wherein the further line is provided at or near ends of the headers remote from the outlet ends. 8. An oil/gas production manifold as claimed in any preceding claim, wherein the manifold comprises first and second headers each of which is controllably communicable with ten production wells. 9. A method of collecting oil/gas produced from at least one production well into a manifold, wherein the manifold comprises first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line. 10. A method of testing production from an oil/gas well fed via a production manifold comprising first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line, the pigging line having a valve therein, the method comprising closing the valve, controllably communicating the well with the first/second header and controllably communicating any/all other wells with the second/first header. 11. A method of pigging first and second oil/gas production pipelines, each pipeline being connected to an outlet end of a respective first/second header of a production manifold, the manifold comprising first and second headers each of which is controllably communicable with at least one production well via control means, an outlet end of each header being connectable to a respective pipeline, wherein the headers are connected to and communicable with one another by a pigging line, the pigging line having a valve therein and the outlets having respective valves provided at or near thereto, the method comprising closing the respective valves, opening the valve in the pigging line and launching a pig down the first/second pipeline through the pigging line and up the second/first pipeline. 12. An oil/gas product manifold as hereinbefore described with reference to Figs 2 and 3.

Inventors: ROBERTSON JOHN GORDON, ROBERTSON, JOHN, GORDON
Applicants: CONSAFE ENG UK LTD, ROBERTSON JOHN GORDON, CONSAFE ENGINEERING (UK) LIMITED, ROBERTSON, JOHN, GORDON
Application year: 1994
Main classification: E21B43
IPC codes: E21B43